The present invention relates to a solenoid for an electromagnetic valve which is mounted to an electromagnetic valve to drive a valve member for switching flow paths.
As shown in FIG. 7, an electromagnetic valve 50 which has been previously proposed by the present applicant comprises a valve portion 51 provided inside with an unillustrated valve member for switching flow paths and a solenoid portion 52 which is connected to the valve portion 51 to drive the valve member, and the valve member of the valve portion 51 is constituted so as to be opened/closed according to pushing effected by a push rod 60.
The solenoid portion 52 is constituted by assembling, in a cylindrical magnetic body case 53 provided at one end with an opening connected with the valve portion 51, a bobbin 55 having a coil 54 wound around an outer periphery thereof, a magnetic body plate 59 which has been attached to an end side of the opening of the magnetic body case 53, a fixed iron core 56 and a movable iron core 58 which have been inserted into central holes of the magnetic body plate 59 and the bobbin 55, and a return spring 57 which biases the movable iron core 58 in a direction in which the movable iron core 58 is separated from the fixed iron core 56 to push the push rod 59.
Then, when the coil 54 of the solenoid portion 52 is energized, as shown on a right half in FIG. 7, the movable iron core 58 is attracted to the fixed iron core 56 to be retracted so that pressing on the push rod 59 is released. When the coil 54 is de-energized, as shown on a left half in FIG. 4, the movable iron core 58 is separated from the fixed iron core 56 by biasing force of the return spring 57 to press the push rod 59, so that the valve member is driven in an interlocking manner therewith.
Now, the magnetic body case 53 generally has a cylindrical skirt portion 53a surrounding a side face of the bobbin 55 and a cap portion 53b covering one end of the skirt portion 53a, where these portions are formed in an integral manner. That is, it is common to punch a member having a shape where these skirt portion 53a and cap portion 53b have been developed integrally in a continuous manner out of a base plate to bend and fold the member in a predetermined shape. However, since the shape of the member where the skirt portion 53a and the cap portion 53b have been developed integrally in a continuous manner is complicated, waste of the material increases when the member is punched out. Also, even when the member is folded and assembled after punched out, since the member must be folded in plural directions and opposed ends must be joined to each other, the number of working steps increases, which results in increase in cost.
On the other hand, in case that the magnetic body case is cylindrical, it is possible to form the magnetic body case by performing a deep drawing of a magnetic base plate. In case that such a working is performed, such a problem occurring at the punching work can be avoided. However, in a case of a non-cylindrical magnetic body case, it is difficult to perform the deep drawing work. For example, when the sectional shape of the movable iron core or the fixed iron core is formed in an elliptic shape including an oval for the purpose of improving the performance of a solenoid or the like, the sectional shape of the bobbin on which the coil has been wound becomes elliptic, so that the magnetic body case must be formed in such a sectional shape as a rectangle so as to correspond to the elliptic shape. However, it is difficult to form a magnetic body case with such a shape by the deep drawing work.
An object of the present invention is to form a magnetic body case in a solenoid for an electromagnetic valve easily at a low cost without any waste of material and with a reduced number of working steps even in case that the sectional shape of the magnetic body case is circular and even in case that it is non-circular such as rectangular.
In order to solve the above problem, according to the present invention, there is provided a solenoid which is mounted to an electromagnetic valve to drive a valve member for switching flow paths. This solenoid comprises: a bobbin which has an iron core hole extending in an axial direction thereof at a center and which has a coil wound around an outer periphery thereof; a magnetic body case which is provided with a cylindrical skirt portion which surrounds a side face of the bobbin and a cap portion covering one end face of the bobbin in the axial direction; an annular magnetic body plate which is connected to an inside of the magnetic body case on the side of the other end face of the bobbin; a movable iron core which is movably received in an iron core hole positioned at centers of the bobbin and the magnetic body plate; a fixed magnetic pole member which attracts the movable iron core; and a return spring which biases the movable iron core in a direction of separating from the fixed magnetic pole member, wherein the skirt portion and the cap portion in the magnetic body case are formed individually of each other, and the magnetic body case is assembled by coupling the cap portion into one end of the skirt portion in the axial direction.
According to the present invention having such a constitution, since the magnetic body case is assembled by forming the skirt portion and the cap portion of the magnetic body case individually and coupling the cap portion to one end of the skirt portion, even when the magnetic body case has any sectional shape, it can be formed easily at a low cost without waste of material and with a reduced number of working steps as compared with a conventional method.
In the present invention, preferably, the thickness of the cap portion in the magnetic body case is larger than that of the skirt portion.
Also, according to the present invention, the cap portion of the magnetic body case has a fitting portion whose shape and size are equal to an inner side shape and inner side size of the skirt portion, and the skirt portion and the cap portion are mutually coupled to each other by fitting this fitting portion to the end portion of the skirt portion.
Furthermore, in the present invention, the sectional shapes of the iron core hole and the movable iron core can be made elliptic and the outer shape of the magnetic body case may be made rectangular.
According to one embodiment of the present invention, the cap portion of the magnetic body case and the fixed magnetic pole member are formed as members separated from each other, they are joined integrally by welding, and the fixed magnetic pole member is fitted into the iron core hole.
According to another embodiment of the present invention, the cap portion of the magnetic body case and the fixed magnetic pole member are formed integrally from the same material, and the fixed magnetic pole member is fitted into the iron core hole.
According to still another embodiment of the present invention, the cap portion of the magnetic pole case also serves as the fixed magnetic pole member, and it has a magnetic pole face for attracting the movable iron core at its portion covering the iron core hole.